1. Field of the Invention
The present invention relates to an anti-glare hard coat film. More particularly, the present invention relates to an anti-glare hard coat film which can provide the excellent anti-glare property without decreasing the highly fine quality of displayed images, exhibits excellent visibility when it is used for various displays such as liquid crystal displays (LCD), plasma displays (PDP), cathode ray tubes (CRT) and touch panels, and is also advantageously used as a protective film due to a great surface hardness.
2. Description of Related Art
When a display such as CRT and LCD is used, light from the outside is occasionally reflected at the surface of the display (so-called glare) and difficulty arises in watching images on the display. In particular, as the size of flat panel displays increases recently, solving the above problem is becoming more important.
To solve the above problem, various methods for preventing glare have been used for various types of display. As an example of such methods for preventing glare, roughness is formed on the surface of hard coat films used for polarizing plates in liquid crystal displays and protective hard coat films for various types of display. The anti-glare methods for hard coat films can generally be divided into (1) methods in which roughness is formed on the surface of a hard coat film by a physical means during curing for forming a hard coat layer and (2) methods in which a filler is mixed into a hard coat material which is used for forming a hard coat layer.
Between these two types of method, the latter methods in which a filler is mixed into a hard coat material is mainly used and silica particles are mainly used as the filler. Silica particles are used because whiteness of the obtained hard coat film can be kept low, no decrease in the hardness takes place, and dispersion is excellent when silica particles are mixed into a hard coat material.
However, displays are recently becoming highly fine so that a high quality of images can be obtained and the conventional anti-glare methods for hard coat films are becoming insufficient. Although various methods such as introduction of aggregates of particles of colloidal silica into a hard coat layer have been attempted (Japanese Patent Application Laid-Open No. Heisei 10(1998)-180950), further improvement in the distinctness of image is desired.
A scratch-resistant anti-glare film in which an anti-glare layer composed of resin beads having a refractive index of 1.40 to 1.60 and a resin composition of the ionizing radiation curing type is disposed on a transparent substrate film is proposed (Japanese Patent Application Laid-Open No. Heisei 6(1994)-18706). In this anti-glare film, polymethyl methacrylate beads, polycarbonate beads, polystyrene beads, polyacryl styrene beads and polyvinyl chloride beads having a particle diameter in the range of 3 to 8 μm are used as the preferable resin beads. To prevent sedimentation of the resin beads in the coating material, silica beads having particle diameters of 0.5 μm or smaller are added in an amount less than about 0.1 parts by weight per 100 parts by weight of the resin of the ionizing radiation curing type.
In the publication of the above technology, fine particles of a silicone resin are not mentioned at all although typical resin beads having a relatively great particle diameter are dispersed in the anti-glare layer to provide the anti-glare property. The silica beads are added in a small amount to prevent sedimentation of the resin beads in the coating material and do not contribute to improvement in the anti-glare property at all.
A light diffusion sheet (an anti-glare sheet) in which a resin film layer having fine roughness on the surface is disposed on at least one face of a transparent substrate film is proposed (Japanese Patent Application Laid-Open No. 2002-107512). In this technology, fine particles are dispersed in the resin film layer to provide fine roughness on the surface of the resin film layer. As the fine particles, inorganic fine particles, organic fine particles and silicone-based fine particles can be used and organic fine particles are preferable. Polystyrene beads and melamine beads are used as the fine particles in the examples and silica beads and silicone particles are used as the fine particles in the comparative examples. This suggests that silica beads and silicone particles are not preferable for providing the anti-glare property.